'Enable Wi-Fi' greyed out

Hi.

I installed Lubuntu (18.04,1 LTS, kernel 4.15.0-34-generic i686) on an old Lenovo X100e ThinkPad and I can't get the wi-fi working. There is no external hardware switch and I can't install windows, so I bought a USB wireless adapter, but still no joy. I've seen many threads for this already, and followed the steps as best I can (for example https://ubuntuforums.org/showthread.php?t=1895671, which led to a bug https://bugs.launchpad.net/ubuntu/+s...ux/+bug/782137). I can see the devices in the System Information panel, but for some reason 'rfkill list all' only shows '0: phy0: Wirelass Lan', which is hard blocked, and no amount of 'sudo rfkill unblock all' changes the status. I have reached the limit of my expertise, and would be extremely grateful for any further suggestions.